1. Field of the Invention
The present invention relates to a method and a system for interconnecting two three-phase alternating electrical networks operating asynchronously or synchronously at alternating voltages of equal or adjacent frequencies.
2. Related Art
In this technical field, it is known that most of the systems for interconnecting two different alternating electrical networks presently in operation are formed by interconnection ties comprising electrical power converters carrying out from one network to the other an AC - DC - AC conversion of the electrical current. Such an interconnecting system has the disadvantage of using compensators for neutralizing the internal reactive power in order to maintain the voltage at the interconnecting points at a desired level, as well as using filters for attenuating the harmonics generated by the interconnecting system.
Another known system, which can be used for interconnecting two alternating networks operating at different frequencies, is described in U.S. Pat. No. 3,275,838 (ALSTROM) granted to ASEA on Sept. 27, 1966. This interconnecting system comprises two electrical current converters connected to the two alternating networks, respectively. A regulating device measures the respective frequencies of the two networks, as well as the power transmitted from one of the two networks to the other network, and acts on at least one of the two converters for controlling and maintaining at a desired level the transfer of electrical active power from one network to the other. Such a system requires the use of a complex circuit and a conversion of the electrical current.
U.S. Pat. No. 2,218,383 (HERSKIND), granted to the GENERAL ELECTRIC COMPANY on Oct. 15, 1940, illustrates a system for interconnecting two alternating networks operating at different frequencies. Such an interconnecting system is provided with a circuit comprising transformers, electrical valves, a phase converter and other elements for obtaining a transfer of electrical power from a three-phase network to a single-phase network, the three-phase network operating at a frequency higher than the frequency at which the single-phase network operates. Obviously, this type of interconnecting system is not adapted for establishing a desired transfer of electrical power between two three-phase, asynchronous or synchronous alternating networks.